The North’s development was characterized by a common system of free labour, commercial vigour, and agricultural diversity. In the 19th century transportation developed markedly along east-west lines; e.g., the Erie Canal opened up the Great Lakes in 1825, and New York City was connected to Chicago by rail in 1852. Thus, both immigration and trade bound northern sections together, creating a remarkable homogeneity of ideology, political and educational institutions, cultural ties, and economic patterns.

By the 1850s the question of the extension of slavery into the western territories was the central issue uniting the North and bringing it into conflict with the South. On the eve of the American Civil War (1861), there were 19 free and 15 slave states, the boundary between them following the Mason and Dixon Line, the Ohio River, and latitude 36°30′ (except for Missouri). The North attained its highest self-consciousness as a region during the war, when its name became synonymous with the Union. Including the four border states that fought with the Union, the North at this time had a population of 22 million, produced 75 percent of the nation’s wealth, and possessed 81 percent of its factories.

The North attempted, largely unsuccessfully, to ensure the political enfranchisement and socioeconomic equality of blacks in the South during the Reconstruction period (1865–77). Meanwhile, the North itself was experiencing an unprecedented period of economic growth as it underwent industrialization. As the 19th century progressed, the North, particularly the Middle Atlantic states and the Great Lakes area of the Middle West, became more and more typified by big cities, big business, and big industrial complexes. Its ample natural resources, excellent inland-waterway system, and proliferating railways confirmed the North as the economic hub of the country, while the vast expanse of prairie and plain on both sides of the Mississippi gave the western reaches of the North the agricultural dominance that would make it America’s breadbasket.

This dominance, however, was not without its costs. Immigration brought millions of southern and eastern Europeans to northern cities, swelling their populations and providing a cheap source of industrial labour but also causing problems of housing, health, and education. When this wave of immigration slowed dramatically after 1920, it was replaced in the second half of the 20th century by another wave made up of Southern blacks, Latin Americans, and East Asians. During the late 1950s the South was the initial locus of the civil rights movement, but by the late 1960s and ’70s the inclusion of minorities in the political and economic mainstream of the nation was as much a challenge in the North as in the South.

Continuing heavy industrialization had affected the environment, causing water- and air-pollution problems, while the concentration of blacks in Northern inner-city ghettos spawned tension and violence and severely affected patterns of housing, education, employment, and public health. These difficulties, coupled with the decay of the North’s industrial base owing to foreign competition and other factors, contributed to further demographic shifts, notably a significant migration of people from the North to southern and western states. In 1939 the North had 70 percent of the country’s manufacturing establishments within its borders. By the late 1970s this figure had fallen to barely more than half. Likewise, the North accounted for 58 percent of the total population of the United States in 1940, but only 40 percent at the turn of the 20th century. Efforts at renewal and revitalization were undertaken by many Northern cities, with varying effect.

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...and white children. In the South, state laws and local ordinances placed limits on the use of public facilities by African Americans and forbade athletic competition between blacks and whites. In the North, African Americans were not usually segregated by law, but local custom dictated second-class citizenship for them.

At first glance it seemed that the 23 states that remained in the Union after secession were more than a match for the 11 Southern states. Approximately 21 million people lived in the North, compared with some nine million in the South of whom about four million were slaves. In addition, the North was the site of more than 100,000 manufacturing plants, against 18,000 south of the Potomac River,...